About Rationally Speaking

Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Thursday, May 28, 2009

Men’s biological clock and IQ: much ado about nothing

“The men are getting really angry and the women are a little too gleeful,” wrote New York Times columnist Lisa Belkin commenting on the overwhelming response she got for an article on a new study that found that men, too, may have a “biological clock” ticking when it comes to having what biologists would call “high quality” offspring.

The headlines reporting the study make ominous pronouncements along the lines of “Older fathers may mean lower IQs in their children,” a conclusion that brings Belkin so far as “[to] hope that somehow it equalizes relationships of sexes.” Couples all over the world are reacting to the news the best they can. CNN reporter Jason Carroll quotes a couple in their late ‘30s saying “We’re having our first. If he is a little less intelligent maybe the world doesn’t need smarter people, doesn’t need more gifted people just deeper people. So hopefully he will be a deep person.” (Hmm, what does it mean to be “deep”? And where is the evidence that the world doesn’t need smarter people?) To this add the predictable commentary of experts like Dr. Harry Fisch (a professor of urology, quoted by CNN), who — while cautioning that the 33,000 children analyzed in the study are of age 7 and below — said that “what we’re seeing are real indications, we’re seeing real clues that as men get older there are problems.”

Oh really? To begin with, it turns out that the Australian study found a difference of only 6 points between children fathered by men in their ‘20s and those in their ‘50s. Moreover, when reading the not-so-fine print of the papers, one finds out that the difference dropped to a miserly 2 points as soon as socioeconomic factors where accounted for. Not exactly an earth shattering discovery, even if one were to think of IQ as a fixed measure of genetic potential. But of course IQ is anything but.

IQ testing was invented by the French psychologist Alfred Binet, originally with the intention of identifying children who may be encountering difficulties during their early education so that they could be given special attention. Of course, the test was soon used for all sorts of bizarre discriminatory practices, particularly against (legal) immigrants in the United States, as detailed in Stephen Gould’s The Mismeasure of Man (e.g., the tests were given in English to people who did not speak English, to “prove” that non-Anglo-Saxon immigrants were clearly stupid and should be kept out of the country).

Even though cognitive scientists are still not quite sure what exactly IQ measures, it is of course a quantitative assessment of some cognitive ability. As with any human trait, a component of it is “heritable” (meaning that there is a statistical covariance between parents and offsprings in terms of their respective IQ — this is far from the everyday meaning of the term heritability, we are not talking about a simple-minded concept of “intelligent genes”).

However, Richard Lewontin, in a classic paper published in 1974 (“The analysis of variance and the analysis of causes,” American Journal of Human Genetics, 26:400-411) has shown that the relationship between genetic and environmental effects in shaping IQ and similar traits in humans is exceedingly complex. Indeed, according to Lewontin, sampling a population with a different genetic constitution would dramatically alter the degree to which IQ responds to altered environmental (e.g., educational, socioeconomic) conditions, while changing the environment would paradoxically result in a different estimate of the supposedly genetically fixed quantity of “heritability” (for technical reasons that I cannot go into here, but see my book: Phenotypic Plasticity: Beyond Nature and Nurture. Baltimore, Johns Hopkins University Press). Bottom line: estimates of IQ and its heritability in humans come with a high degree of uncertainty (much, much more than 2 points!) and change dramatically as a function of the environment.

How dramatic? A classic study by Cooper and Zubek in rats (“Effects of enriched and restricted early environments on the learning ability of bright and dull rats,” Canadian Journal of Psychology, 12(3):159-164, 1958) used two genetically selected lines that were respectively very good and very bad at solving maze problems. The authors then raised both “dull” and “bright” rats in very stimulating environments (cages enhanced by color and toys) and in very depressing ones (cages with no color or toys) and compared them again. The results were rather stunning: the environment had completely erased the genetically selected differences between the two lines: dull rats performed as well as the bright ones if grown in stimulating environmental conditions, and vice versa the bright rats did as poorly as the dull ones under deprived conditions. Conclusion: very strong, genetically “determined” differences in intelligence can be erased by a simple change in the environment. Alas, we can’t do the experiment with humans, for obvious logistical and ethical reasons. But there is no rationale to think that we would react much differently, at least qualitatively.

Given all of the above — about which of course you will find not a trace in either the CNN or the New York Times articles covering the aging fathers story — what is the import of an alleged difference of 2 points in the IQ of young children fathered by 20-somethings vs. 50-somethings? To put it bluntly, that difference is in fact completely insignificant (sorry, ladies), and there is no reason for anyone to lose any sleep over this, or worse, for men to rush into having babies in order to keep up their children’s chances of getting into Harvard. Besides, we all know that men aren’t very emotionally mature until they get into their 30’s, so why would a woman wish to have a child with someone who is still himself a baby? Now, there is something that requires serious study.

Unless all of the mothers in this study were exactly the same age, I don't see how they can ascribe the effects to just the father. I'm guessing that the older fathers, on average, had older female partners.

And Jordan, I don't know that you should rush out and start reproducing like a rabbit but there are some advantages (besides any possible effect on IQ) to having kids while you are younger. Energy level is one. Try keeping up with a 10 year old when you're 55 as compared to when you're 35. Getting them educated and out on their own is another. Have a child when you are 55 and she's not moving out until you are 75 or 80. On the other hand there are some advantages to waiting a bit. You are generally more mature and settled moving into your late 30s and 40s and you are probably better off financially.

I remember reading about this in New Scientist a while back. The NS article also mentioned "increased risk of schizophrenia, autism and bipolar disorder in the children of older dads." So it isn't just IQ.

As for mothers, they find that the child's IQ increases with age at which the mother bore him/her.